# define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
	double sum = 0;
	for (int i = 1; i <= 100; i+2)
	{
		sum += (1.0 / i);
	}
	for (int j = 2; j <= 100; j + 2)
	{
		sum -= (1.0 / j);
	}
	printf("%lf", sum);
	return 0;
}